An electrically connecting structure such as an interconnection for connecting elements between semiconductor devices is becoming more critical as the sizes of the devices are scaled down. Typically, the interconnection or other electrically conducting elements are widely used for providing specific conducting paths in an electrical circuit. In the process of forming the electrical conducting structure over an underlying layer, it is important that the surface of the underlying layer be free of any contamination, such as moisture, particles or oxides. Further, the surface of the underlying layer must be planar for subsequent layer deposition.
Tungsten is one of the common materials used in the formation of an electrical conducting structure. Before forming a tungsten layer over a underlying layer, a composition layer consisting of Ti and TiN layers must be formed along the surface of the underlying layer to act as a barrier layer. A rapid thermal annealing step is subsequently employed after the barrier layer is formed. However, the so called "micro-crack" phenomenon will occur after rapid thermal annealing. The phenomenon is attributed to stress release for the barrier layer. In the conventional method, the tungsten layer can be deposited by using chemical vapor deposition on the Ti and TiN composition layers. The reaction material for forming the tungsten layer includes WF.sub.6 and SiH.sub.4. Fluorine gas will be generated during the reaction. The fluorine penetrates through the micro-cracks and reacts with the titanium atoms. Thus, a by-product consisting of TiF.sub.x is generated and explodes out of the barrier layer and tungsten layer. This is referred to as the "volcano effect". This effect creates undesired tungsten particles on the surface of the tungsten layer.
What is required is a method of forming a tungsten layer free from particle contamination.